This invention relates to a simple means and method for preventing or, better, obviating the problem of sliver slingover and its waste on starting up the filling of a sliver can with coiled sliver from a high speed drawframe.
Drawframe sliver is most conveniently collected for conveyance to subsequent yarn forming machines by coiling it as it issues from the drawframe into a cylindrical sliver can. To appreciate the present problems in the art which this invention addresses, one must understand that to increase production in order to reduce unit product costs, the art has mechanized and automated its processes and machines leading to yarn making, including collecting sliver in cans. These advances include vast increases in throughput rates of sliver in drawfames, and thus concomitant increases in coiling rates and the collecting of the sliver. In this, sliver coils delivered to the can must be layered to form a pattern from which subsequently the sliver may be withdrawn without snagging or in any other manner disrupting the orientation of the fibers aligned within the strand. To provide the desired economies, can changing or doffing also has been automated so as to quickly exchange a filled can with one to be filled with sliver coils. It then is desirable to make the exchange very quickly in order to reduce the interval during which the drawframe is stopped during the can changing; this has become yet more and more important with the substantial shortening of the time in which it takes to fill a can, thus in all increasing the number of can changings in any given work interval of time. It is usual to stop the feed of drawframe sliver during can changing. Once the empty replacement can is in position, sliver feed from the coiler can be restarted. Here is where the present problems arise.
From the viewpoint of economics, on paper, it is most desirable in start-up to move from no feed to sliver feed at the highest throughput rate possible in the least time. Prior to the invention, were one to operate the drawframe and coiler at full operating speeds right from start-up, while the mechanisms would show little if any strain one would note almost immediately processing difficulties. These would appear as loops or loopings of sliver encircling the can's rim as the can was rotated, which loops are known in the art as sliver "slingout" or even more commonly as sliver "slingover." Slingover is due to the unrestrained slinging out or spewing forth of sliver upon start-up at high speeds and thus high moments of inertia. While it is possible to minimize slingover by, with great care, selecting sliver cans which have rugged springs thrusting upward the can's piston or false bottom into abutment with the underside of the coiler plate, and thus to provide resistance to the uncontrolled slingout of sliver and contain it within the perimeter of the inner walls of the can, such selection and care are expensive and in the push for economies are often eschewed. Another tactic used to avoid sliver slingover is to significantly reduce the otherwise high moments of inertia of the sliver spewed out on start-up at full production speeds by significantly reducing the speed of sliver or throughput rate.
The significance of the problems of sliver slingover is easily understood when one views what happens upon withdrawal of sliver from the can such as during feed of an open end rotor spinning machine. The coiled sliver is set down in a patterning so that the single sliver strand which makes up the contents of the can may be withdrawn from the can smoothly, and with a minimum disturbance of the ordered array of aligned fibers within the strand; any disturbance of the alignment of the fibers causes irregularities in the strand and ultinately in the yarn product obtained. The loopings of sliver produced by sliver slingover upon start-up are drawn down back into the can along its inner walls as the can fills with its patterned array of coils, to cause a "scuffing" of the coils of sliver that the drawn-back loops may come into contact with, imparting even some intermingling of fibers from the loops and fibers from the coils. Then, upon withdrawing sliver from the can, such as in the feed of an open end machine, a mess can be created causing the sliver to become waste and shutting down the spinning station or delivery. Readily one may appreciate what such circumstances do relative not only waste sliver but also how they adversely affect the rate and costs in yarn production.
The two approaches just mentioned to obviate slingover have not been deemed to be satisfactory in commercial usage. Selection and use of only those cans having proper springs of sufficient strength and force have proven to be unrealistic; also, the reduction of start-up speeds much below ordinary production speeds works in a direction opposite the goal of maximizing production rates.